A sentinel lymph node is a lymph node that is first reached by cancer cells from a tumor via lymph flow and is the lymph node with the highest possibility of metastasis by the cancer cells. Thus, if the sentinel lymph node is identified correctly and if metastasis by cancer cells is not found therein, it can be considered that there is no metastasis to other organs. Significant reductions in physical and psychological burdens placed on a patient, restraining of treatment costs by omission of ablative surgery, etc., are thus anticipated.
As methods of detecting the sentinel lymph node, dye methods and RI (radioisotope) methods are mainly known. With a dye method, for example, a blue dye, such as indigo carmine, is injected close to a tumor, the lymphatic duct that is dyed in blue is traced visually, and the lymph node that is reached first is detected as the sentinel lymph node. With the RI method, for example, a radioisotope that serves as a tracer is injected close to a tumor, a living body observation portion that is presumed to include the lymph node, at which the radioisotope first arrives and accumulates, is probed from above the skin by a gamma probe, and the living body observation portion at which gamma rays are sensed is detected as the sentinel lymph node.
Methods of identifying a sentinel lymph node using a fluorescent dye have also been proposed. With the sentinel lymph node detecting apparatus disclosed in Patent Document 1, a fluorescent dye is injected close to a tumor in advance, and light of a predetermined wavelength is illuminated as excitation light onto a living body observation portion that is presumed to include the sentinel lymph node in the periphery of the tumor. Identification of the sentinel lymph node is then carried out by converting and displaying a fluorescence image of the near-infrared wavelength band that is generated from the living body observation portion, to and as a visible image.    Patent Document 1: Japanese Patent Application Laid-Open No. 2001-299676